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, v H. s. OSBORNE; MEANS FOR AND METHOD OF AVOIDING INTERFERENCEAPPLICATION nuzo' IULYBI. 1918; 1 432 7 Patented Oct. 24, 1922.

c $9 I Q I g i I I E Q U -I**-r Q I I M I Q- JL I I' Q I I I I I I l I II I I I I I [1, Q y v v V V V INVENTOR. H 5. Osborne BY mama/3% ATTORNEY40 conditions to be met.

Patented Oct. 24, 19 22.

mom) s osiaoann'or NEwfYoRx, N. Y., assionon TO AMERICAN TELEPHONE ANDUNITED, STATES 1,432,781 PATENT OFFICE.

TELEGRAPH COMPANY, A CORPORATION OF NEW YORK.

Imus on AND METHOD E AVOIDING INTERFERENCE.

"Application filed na 31,

cuits of ocean cables and is here illustrated 1 and described-as appliedto such a=circuit,

1 but it is to be understood that its usefulness is not limited thereto;e l 7 As is well known, the signal impulses received over ocean cablesare extremely weak and difficult to record as compared with ordinalandline signals and it is customary F to re uce the disturbances in thecable circuits by grounding thereturn circuit at a point at sea, oftenseveral miles distant instead ofiat the cable 'oflice. Thisavoids dis-'turbainces due to local ground-potentials. It does not, however,entirely eliminate disturbing influences because the conductors runningfrom the cable office to the cable and to the sea ground, respectively,ma be 80 subject todisturbingpotentials induce nei hboring powercircuits or the like. t

is t e object of the present invention to provide meansfor overcomingthese difiicul- 85 The invention will be more fully understood by areference to the accompanying drawings in which'Fi re 1 illustratesdiammatically one em 'diment thereof and i 12. '2'represents a circuitillustrating the Fig. 1 shows diagrammatically the ordinary terminalconnections for duplex operation of a cable circuit, wherein the cable 1is'connected to the apparatus 2 in the cable as bfiioe by a conductor3- 1. The recording apparatus 5 is connected between the conductor 3-4and the artificial line ,6, in parallel with the ratio arms 7 and 8'which provide the connecting point for one side of the sendinapparatus9,*'the other side being groun ed, all as is customary induplex cableoperation. Instead of ounding the artificial line ,6 andthesending apparatus 9 locally, 'it is common as above indicated to 56connectthern metallically with asea ground 1918. 'Serial No.24 7,608.

to avoid local disturbing potentials. Such a ground connection isindicated on the draw ings at 10, with a conductor 1112 extendingbetween the cable oifice and the sea Y i a r so I The conductors 34l and11-12 maybe ground.

subject to disturbing potentials, and due to the unbalanced condition ofthe circuit with; respectto such potentialsthey will beevi-' den'ced. 1nthe receiving apparatus5 to" the 1 confusion of transmitted signals. For instance, in the system illustrated in Fig. 1, it maybe supposed thata disturbing potential is caused in that sectionoi the conductors 3-4and11-'12 lying betweenthe dotted lines a-b and -0cZ. This potentialwill ordinarily be of the same sign and magni- 1 pacity to groundthroughout its length andmore or less leakage, the induced potentials a"and y if equal would not afiect the receiving apparatus 5 since theywould neutralize each other therein. For the purpose of illustrating theeffect of the leakage and capacity to ground, we may imagine each of thecircuits 34 and 11-12 to be" connected, at the points 3 and 11respectively, to the common ground 13 through like impedances 14 and 15,as indicated in Fig. 2. The 0pposite end of the conductor Lil-12 isgrounded at 10, (the-sea ground) while the opposite end of the conductor3- 1 reaches ground 17-only after passing through the entire cable 18which is of high impedance as compared with the ground 10. Considering,then, the admittance to ground of conductors 3- 1 and 1112 thepotentials a: and y are applied to parallel circuits which maybe'traced, respectively as follows a 4, 3, 141, 13, 17, 18, 1 and 12,11,15, 13, 10, 12. The potential y is consumed entirely by the impedanceof the circuit 11-12 andthe' impedance 15, the point 12 and ground-10being regarded as electrically the same for the purposes of thisillustration. The potential w is consumed in the impedance of thecircuit -i-3 and impedance 14, which are equal to the correspondingimpedances of the other circuit, plus the impedance of the cable 18. Itis, therefore, obvious that the voltage drop across the impedance 15will be greater than the voltage drop across the impedance 14; and sincethe two impedances are connected to the common ground 13, which may beregarded as at zero potential it will be obvious that the point 11 willhave a higher potential than the point 3 and that a circuit connectedbetween 11 and3, such as the receiving circuit 5 in Fig. 1, will receivea current due to this difference of potential.

To correct this condition it is necessary to so vary theimpedancebetween one side 01" the line and ground that the two terminals arebrought to the same potential for all frequencies employed. For thispurposeit is necessary that the impedance 3-17 (referring to Fig. 2) beto the impedance 1110 as impedance 14 is to impedance 15. In a case thensuch as illustrated. in Fig. 2 where 3-17- excee ds ill-10 the impedanceat 15 must be made less than. the impedance at l l. A convenient methodof accomplishing this result in the ordinary cable circuit is to connectan impedance between the point 11 and ground as indicated in Fig. 1. Thecharacter of this connection will depend upon the character of thecircuit with which itis used. Where the impedance to be balancedconsists of resistance and capacity as it-frequently will in oceancables this shunt will consist of like elements-as illustrated in Fig.1, where use is made of a resistance 20 in series with an artificialline 21 the latter comprising resistance and shunt capacity It will beclear. from an inspection of the drawing that such a shunt connectedbetween the point 11 and ground will reduce the impedance between thesepoints and will therefore decrease the potential drop. between them, andif properly proportioned will. reduce the potential of the point 11 tocorrespond with that of the point 3 with the result that no current willflow in a cir cuit connected between them due to the in: ducedpotentials 0c and y.

It should be understoodthat the cl P1311031? tion of the invention isnot limited to the case where the potentials and y are equal but in anycase where they are known the proportion above mentioned between the impedances can be varied to satisfy. conditions by adding or subtractingimpedance at the proper points as will be obvious.

It will be understood, of course, that, in the actual circuit theimpedance indicated at 14 and .15 in Fig. 2 are distributed along theentire length of the conductors 34 and 11-12, but the principle by whichthe shunt affects the correction remains in general the same.Theoretically the shunt should be connected at the midpoint of theimpedance represented by the conductors 3-4L and 11-12 but since thepoint at which the disturbances may arise will vary from time to time,no definite point for the connection of the shunt 19 can be assigned andit has been found that the connection of the shunt close to the point 11will substantially equalize the potentials at 3 and,11;.itor all inducedpotentials likely to be metpand throughout a. wide range of frequencies.In general the resistance 20 of the shunt 19 should have a magnitude.

Experiments show that in the average ocean cable system, a longartificial. line at 21 is unnecessary, a. total product of capacity andresistance (K. R), of 0.013 giving practically asgood results as largervalues. A shorter cable than. this, however, gives less perfectneutralization. V

The operation ofv the system. will be obvious from the foregoingdescription. It the points 3 andll arebrought-to the same potential, nocurrentwill fiow through. the apparatus of the cable ofiiceconnected tothese pointssince whatever is includedin. the circuit from thereon willhave equal and opposite potentials applied'thereto. Ifthere is capacitytoground or substantial leakage in the artificialline 6 or otherelementsot' the sending and receiving apparatus, there would be someunbalance in receivinginstrument 5,

but ordinarily any such leakage or capacity to ground is so small thatit may be disregarded. Actual tests with a shunt connection to, thecircuit, as herein described, show that the disturbances in thereceiving instrument 5 are reducedby about ninety per cent.

It is to be understood that. the invention is not, limited to theparticular circuits hereinshownand described and it will be obvious tothose skilled in the art that modifications in details may be madewithout departing t'romthe spirit. of the invention.

What is claimedisz- 1.1n a signal transmitting system, a metallictransmission line, a duplex set for sending and receiving signalsthereover ineluding an artificial line between which and the main linethe receiving instrument of the set is connected, a conductor connectingthe duplex set with the ocean cable, a second conductor connecting thetransmitting dedisturbing outside sources.

2. In a signal transmitting system, a metallic transmission line, aduplex set for sending and receiving signals thereover including anartificial line between which and the main line the receiving instrumentof the set is connected, a conductor connecting the duplexset with theocean cable, second conductor connecting the transmitting device of theduplex set and the artificial line with ground, a shunt between saidsecond named conductor and ground and comprising a resistance and anartificial line, for equalizing voltages at the terminals of said duplexset due to potentials induced in said conductors by disturbing outsidesources.

In testimony whereof I have signed my name to this specification thisthirtieth day of July, 1918.

HAROLD S. OSBORNE.

